Electric trains are generally supplied with electric energy via cables. Also with regard to automobiles, it is similarly proposed to supply electric energy to a vehicle from road facilities through microwaves.
Japanese Patent Laying-Open No. 2006-174676 (Patent Document 1) discloses a non-contact power feed system using microwaves as described above. In this system, the vehicle is provided with a power storage device, in which the electric power transmitted from road facilities to the vehicle is determined based on the torque command value, the state of charge of the power storage device and receivable electric power through microwaves.
Furthermore, three technologies are known as promising wireless electric power transmission technologies such as electric power transmission using electromagnetic induction and electric power transmission by the resonance method, in addition to electric power transmission using radio waves such as microwaves.
Particularly, the resonance method utilizes the resonance in the electromagnetic field for electric power transmission, by which a large electric power of several kW can be transmitted for a relatively long distance (for example, several meters) (see Non-Patent Document 1).